<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>移动网页</title>
</head>
<body>
    <div class="main">

    </div>
</body>

<style>
    .main{
        width: 800px;
        height:300px;
        margin: 0 auto;
        background-color: aqua;
    }

</style>    
</html>